Yeah.
Low CYA with full sun will drop your chlorine a lot during the day.
Without a feeder, you probably need to take the CYA on up, so you can start the day with 6 ppm and end with 3 ppm.
Unfortunately, the reappearing stain is probably not really leaving in the first place -- it just changes form, depending on conditions in the pool.
PoolDoc

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) Bleach, borax and baking soda just happened to be what's available at the grocery store in generic form. "CHBB" is not as catchy, but if cal hypo were available at the grocery store, that page could have been titled "Cal hypo, borax, and baking soda".

